This disclosure relates to methods of servicing a wellbore. More specifically, it relates to servicing a wellbore with viscosified treatment fluids and breaker compositions.
Natural resources (e.g., oil or gas) residing in the subterranean formation may be recovered by driving resources from the formation into a wellbore using, for example, a pressure gradient that exists between the formation and the wellbore, the force of gravity, displacement of the resources from the formation using a pump or the force of another fluid injected into the well or an adjacent well. The production of fluid in the formation may be increased by hydraulically fracturing the formation. That is, a viscosified treatment fluid (e.g., a viscosified fracturing fluid) may be pumped down the wellbore at a rate and a pressure sufficient to form fractures that extend into the formation, providing additional pathways through which the oil or gas can flow to the well.
A variety of other viscosified treatment fluids besides viscosified fracturing fluids may also be used in subterranean applications, such as for example drilling fluids and gravel packing fluids. Oftentimes, after the viscosified treatment fluid has performed its desired task, it may be desirable (for example, in order to minimize or eliminate any damage to the formation permeability due to polymer penetration) to reduce its viscosity (e.g., “break” the fluid) so that the treatment fluid can be recovered from the formation and/or particulate matter may be dropped out of the treatment fluid at a desired location within the formation.
Internal breakers, such as enzymes, oxidizers, acids, or temperature-activated viscosity reducers, can be used to reduce the viscosity of viscosified treatment fluids. Unfortunately, these traditional breakers may result in an incomplete and/or premature viscosity reduction. Premature viscosity reduction is undesirable as it may lead to, inter alia, particulates settling out of the fluid in an undesirable location and/or at an undesirable time. Moreover, conventional non-delayed breakers begin to reduce the viscosity of the viscosified fluid upon addition and continue to reduce the viscosity of the fluid with time until the fluid is completely broken or until the breaker is expended. Since the breaking activity begins immediately, it is common practice to start with excess viscosifier to offset the point at which the viscosity falls below an acceptable level. Using excess viscosifier is not only an added material expense, it also may lead to increased or excessive friction pressure during treatment placement, thereby further increasing the required pumping capacity and associated operating expense. Alternately, encapsulated breakers may be used to control the release rate of breaker. Such options, however, add to material costs.
As an alternative to using traditional breakers, breaking a viscosified treatment fluid may also be accomplished using just time and/or temperature. The viscosity of most treatment fluids will reduce naturally if given enough time and at a sufficient temperature. However, such methods generally are not practical as it is highly desirable to return the well back to production as quickly as possible, as opposed to waiting for the viscosity of a treatment fluid to naturally decrease over time. The task of breaking the viscosified treatment fluids is also a problem at many of the lower temperature wells (e.g., bottom hole temperatures of about 130° F. or lower). Catalysis of the breakers (e.g., breaker activation) is often employed to improve breaking of the fluid, but finding a suitable formulation that meets all performance criteria is often a challenge. Thus an ongoing need exists for improved compositions and methods of breaking viscosified treatment fluids.